1. Field of the Invention
The present invention relates generally to a communication system, and more particularly to a communication device and a transit device having a call-hold function and a method for controlling the call-hold function.
A technique, called the Internet Telephony, is spreading rapidly in recent years to perform a voice communication by storing voice information in an Internet Protocol (abbreviated to IP) packet as a means to integrate voice with data.
Such services as call hold, call transfer and call diversion are being studied and stipulated recently by the International Recommendations as the supplementary services of the Internet Telephony voice services. The present invention is related to this call hold, which offers such services as to interrupt a speech temporarily and give a holding tone.
Accordingly, an apparatus and a method for performing the call-hold operation effectively and economically is in great demand.
2. Description of the Related Art
The Internet Telephony (or Voice Over IP: VoIP) provides voice services by using the IP message. FIG. 1 shows a configuration of the Internet Telephony system.
An Internet telephone (IP-TEL) or a personal computer (PC) equipped with a microphone (MIC) and a speaker (SPKR) to realize a telephone function performs voice communication by storing voice information in the IP message transmitted in an IP network of a local area network (LAN). It also performs voice communication in the same way over different LANs through a digital exchange network (DGTL EXCH NTWK) and a router for routing a packet in the network.
The IP-TEL and PC (hereinafter, generally called End Point: EP) convert voice information into an IP packet and transmit the packet to the IP network, and also receive an IP packet from the IP network and convert the packet into voice information to output as an audible sound.
A Gate Keeper (hereinafter abbreviated to GK) stores therein and manages the EPs' addresses within the IP network, i.e., IP addresses which correspond to the EPs' telephone numbers (or locally allotted numbers within a LAN) and performs functions such as three-party calling and call diversion.
FIGS. 2A and 2B show system configurations in which the present invention is implemented, wherein an EP (i.e., IP-TEL or PC) performs voice communication directly and through a GK, respectively with a counterpart EP in the Internet Telephony system shown in FIG. 1.
FIGS. 3–6 show the signalling sequence of the call control messages for call set-up, speech, call hold and call disconnect operations conducted on the IP network (refer to ITU-T Recommendations H.225.0 and H.245). The message names conform to the notation used in the Recommendations. There are two call-hold methods stipulated by ITU-T Recommendation H.450.4: method 1 (Near-End Call Hold method) and method 2 (Remote-End Call Hold method).
FIGS. 3 and 4 show the signalling sequence according to methods 1 and 2, respectively when communication takes place directly between the EPs. FIGS. 5 and 6 show the signalling sequence according to methods 1 and 2, respectively when communication takes place between the EPs through the GK.
In a case, too, where communication takes place between the EPs belonging to different LANs, the signalling sequence is the same except that the signals go through a digital network existing between the LANs as shown in FIG. 1. The call hold occurs in the period shown by * in the figures, during which speech is in progress.
FIGS. 7A and 7B show the format of an IP message transmitted within the IP network (for details, refer to the ITU-T Recommendations enclosed in parentheses in the figure). FIG. 7B shows the details of H.225.0 Q.931 Header shown in FIG. 7A, in which the later-described call-hold request and reply signals exchanged between the EPs are specified in the Information Element Type field as User—User Information.
FIG. 8 shows the detailed message for transmitting voice and holding-tone information, which is specified in the RTP Header shown in FIG. 7A. In FIG. 8, the Source address and Destination address of the IP Header show IP addresses of the call originator (calling EP) and terminator (called EP), respectively in the IP network. The voice and holding-tone information is specified as payload data.
When to communicate via the GK, for example, in the IP network based on the aforesaid International Rules, the calling EP requests the GK to set up a call by specifying the telephone numbers of its own and the destination EP in the H.225.0 Q.931 Header. Since the GK previously stores therein and manages the IP addresses corresponding to the phone numbers of EPs, it can recognize the IP addresses of source and destination EPs. Also, as for the aforesaid call-control message, since the GK knows previously the IP addresses of both calling and called EPs, it can perform the call control.
After completion of a call set-up sequence by using the H.225.0 Q.931 Header, the H.245 Header for controlling voice channel information is transmitted. Under control of the H.245 Header, the destination of the voice information (RTP Header) is confirmed between the EPs. On completing the control by the H.245 Header, the EPs exchange the voice information (RTP Header), bypassing the GK.
FIGS. 9A and 9B show the signalling sequence for controlling call hold. Of the two methods for controlling call hold stipulated by ITU-T Recommendation H.450.4, FIG. 9A shows method 1 (Near-End Call Hold method) and FIG. 9B shows method 2 (Remote-End Call Hold method). Although FIGS. 9A and 9B show an example in which the EPs communicate directly with each other, the signalling sequence between the EPs is the same even when they communicate via the GK, since the GK only relays the call-hold control signals.
In FIG. 9A, while voice communication is in progress, the holding EP transmits the Near-End Call Hold request signal (H.225.0 Q.931 FACILITY[holdNotific.inv] message) to forcibly place the held EP in a hold condition. On receipt of the request signal, the held EP recognizes call hold and enters the hold condition. The holing EP further transmits music/video information to the held EP and based on the information, the held EP gives a holding tone or displays an image indicating a call hold.
In FIG. 9B, while voice communication is in progress, the holding EP transmits the Remote-End Call Hold request signal (H.225.0 Q.931 FACILITY[remoteHold.inv] message) to the held EP. The held EP returns the Remote-End Call Hold reply signal (H.225.0 Q.931 FACILITY[remoteHol d.rr] message) and recognizes call hold. Then, the held EP enters the hold condition and generates music and/or video information by itself to provide music on hold and/or display a video image on hold.
Thus, according to the conventional method, when the call-hold method which the holding EP supports differs from that the held EP supports, especially when the holding EP supports only the Remote-End Call Hold function and the held EP supports only the Near-End Call Hold function, it is a problem that call hold cannot be achieved even though both EPs have the call-hold function.